Searching for Anticancer Agents and Antimalarial Agents from Madagascar
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SEARCHING FOR ANTICANCER AGENTS AND ANTIMALARIAL AGENTS FROM MADAGASCAR Ende Pan A thesis submitted to the faculty of the Virginia Polytechnic Institute and State University in partial fulfillment of the requirements for the degree of Doctor of Philosophy In Chemistry Dr. David G. I. Kingston Dr. Paul R. Carlier Dr. Harry W. Gibson Dr. Brian E. Hanson Dr. James M. Tanko (December 8, 2010) Blacksburg, VA Keywords: Natural Products, Anticancer, Antimalarial, Antiproliferative, Flavonoid, Cardenolide, Diphenylpropane, Alkaloid, Sesquiterpene lactone SEARCHING FOR ANTICANCER AGENTS AND ANTIMALARIAL AGENTS FROM MADAGASCAR Ende Pan ABSTRACT In our continuing search for biologically active natural products from Madagascar as part of an International Cooperative Biodiversity Group (ICBG) program, a total of four antiproliferative extracts were studied, leading to the isolation of twelve novel compounds with antiproliferative activity against the A2780 human ovarian cancer line, and one extract with antimalarial activities was studied, which led to the isolation of five new natural products with antimalarial activities against the Dd2 and HB3 malarial parasites. The plants and their metabolites are discussed in the following order: one new xanthone and two known guttiferones from Symphonia tanalensis Jum. & H. Perrier (Clusiaceae); four new diphenyl propanes and one new cyclohepta-dibenzofuran skeleton from Bussea sakalava (Fabaceae); four new cardiac glycosides from Leptadenia madagascariensis Decne. (Apocynaceae); two new and four known alkaloids from Ambavia gerrardii (Baill.) Le Thomas (Annonaceae); five new sesquiterpene lactones from Polycline proteiformis Humbert (Asteraceae). The structures of all compounds were determined by analysis of their mass spectrometric, 1D and 2D NMR, UV and IR spectroscopic and optical rotation data. Other than structure elucidation, this dissertation also involve bioactivity evaluation of all the isolates, synthesis of two interesting alkaloids, as well as a proposal for the possible biosynthetic pathway of the new cyclohepta-dibenzofuran skeleton. ACKNOWLEDGEMENTS Firstly, I would like to thank my advisor, Dr. David G. I. Kingston, for giving me the opportunity to work in his lab at Virginia Tech. I feel grateful for his guidance, patience, concern and kindness throughout my time in Blacksburg. And I would also like to thank the other members of my committee, Drs. Paul R. Carlier, Harry W. Gibson, Brian E. Hanson, James M. Tanko, and the former member, Dr. Larry T. Taylor. Their wisdom, advice and encouragement has been greatly appreciated. Special thanks are given to Drs. Shugeng Cao and Liva Harinantenaina for teaching me so much about natural product chemistry and for providing me invaluable suggestions on research problems. I would like to thank Drs. Paul Roepe and John Alumna at Georgetown University for our collaborative effort on the antimalarial project. Without the help and support from current and some of the former members of Dr. Kingston’s group, the current work would not have been possible. So I would like to thank Ms. Peggy Brodie, Drs. Qiao Hong Chen, Yanpeng Hou, Brian Murphy, Vincent E. Rasamison, Patricia Onocha, Chao Yang, and Jun Qi, Mr. Jielu Zhao, Ms. Yixi Liu, Mr. Alex Xu, Mr. Yumin Dai and Mrs. Melody Windsor. I would also like to thank the current and former departmental analytical service staff Dr. Hugo Azurmendi, Dr. Mehdi Ashraf-Khorassani, Mr. William Bebout, Mr. Tom Glass, Mr. Geno Iannaccone, and Dr. Carla Slebodnick for their assistance. Finally, I could not come so far without love, support and encouragement from my family. I would like to thank my parents, Zexin Pan and Yun Sun for always loving me and supporting me so much over the years. I would like to thank my wife, Xian Wang, who has given up so much and always been there for me all these years. iii TABLE OF CONTENT Page LIST OF FIGURES ix LIST OF SCHEMES xi LIST OF TABLES xii I. Introduction: natural product drug discovery 1 1.1 Introduction 1 1.2 Natural product drug discovery 2 1.3 Natural products medicines from different sources 4 1.4 Anticancer agents and antimalarial agents from natural resources 7 1.5 The ICBG (International Cooperative Biodiversity Groups) program 10 References 12 II. An antiproliferative xanthone and two guttiferones of Symphonia tanalensis from the Madagascar rainforest 16 2.1 Introduction 16 2.1.1 Previous investigations of Symphonia 17 2.2.Results and Discussion 18 2.2.1 Structure elucidation of Compound 2.1 18 2.2.2 Identification of the know guttiferone I and A 21 2.2.3 Antiproliferative activities of isolated compounds 22 2.3 Experimental Section 23 iv References 29 III. Four diphenylpropanes and a cycloheptadibenzofuran from Bussea sakalava from the Madagascar dry forest 33 3.1 Introduction 33 3.1.1 Previous investigations of Bussea 34 3.2 Results and Discussion 34 3.2.1 Structure elucidation of bussealin A (3.1) 34 3.2.2 Structure elucidation of bussealin B (3.2) 36 3.2.3 Structure elucidation of bussealin C (3.3) 37 3.2.4 Structure elucidation of bussealin D (3.4) 38 3.2.5 Structure elucidation of bussealin E (3.5) 39 3.2.6 Possible biosynthesis of bussealin E (3.5) 42 3.2.7 Antiproliferative activities of bussealin A-E (3.1-3.5) 43 3.3 Experimental Section 44 References 48 IV. Cardenolides of Leptadenia madagascariensis from the Madagascar dry forest 52 4.1 Introduction 52 4.1.1 Previous investigations of Leptadenia 53 4.2 Results and Discussion 54 4.2.1 Structure elucidation of madagascarensilide A (4.1) 54 4.2.2 Structure elucidation of madagascarensilide B (4.2) 58 v 4.2.3 Structure elucidation of madagascarensilide C (4.3) 59 4.2.4 Structure elucidation of madagascarensilide D (4.4) 63 4.2.5 Antiproliferative activities of madagascarensilide A-D (4.1-4.4) 64 4.3 Experimental Section 65 References 69 V. Isolation and synthesis of antiproliferative eupolauridine alkaloids of Ambavia gerrardii from the Madagascar dry forest 73 5.1 Introduction 73 5.1.1 Previous investigations of Annonaceae 74 5.2 Results and Discussion 75 5.2.1 Structure elucidation of compound 5.1 76 5.2.2 Structure elucidation of compound 5.2 77 5.2.3 Synthesis of compounds 5.1 and 5.2 77 5.2.4 Antiproliferative activities of compounds 5.1-5.6, 5.10 and 5.11 81 5.3 Experimental Section 82 References 90 VI. Five new antimalarial pseudoguaianolides of Polycline proteiformis from the Madagascar dry forest 95 6.1 Introduction 95 6.1.1 Previous investigations of Asteraceae 95 6.2 Results and Discussion 96 vi 6.2.1 Structure elucidation of polyclinolide A (6.1) 97 6.2.2 Structure elucidation of polyclinolide B (6.2) 100 6.2.3 Structure elucidation of polyclinolide C (6.3) 101 6.2.4 Structure elucidation of polyclinolide D (6.4) 104 6.2.5 Structure elucidation of polyclinolide E (6.5) 105 6.2.6 Structure elucidation of compound 6.6 106 6.2.7 Bioactivities of polyclinolide A-E (6.1-6.5) and centaureidin (6.6) 106 6.3 Experimental Section 109 References 114 VII. Miscellaneous Plants Studied 118 7.1 Introduction 118 7.2 Anticancer extracts 118 7.2.1 Chadsia racemosa (Fabaceae) 118 7.2.2 Gastonia duplicate (Araliaceae) 119 7.2.3 Entada louvelii (Fabaceae) 119 7.2.4 Entada sp. (Fabaceae) 120 7.2.5 Leea guineensis (Vitaceae) 120 7.2.6 Droceloncia reticulate (Euphorbiaceae) 120 7.3 Antimalarial extracts 121 7.3.1 Phyllanthus muellerianus (Euphorbiaceae) 121 7.3.2 Microdemis Caseariaefoli (Pandaceae) 122 7.3.3 Majidea sp. (Sapindaceae) 123 vii 7.3.4 Terminalia septentrionalis (Combretaceae) 124 7.4 Structure elucidation on compounds isolated in Madagascar 124 References 125 VIII. General Conclusions 127 8.1 Anticancer extracts 127 8.2 Antimalarial extracts 128 APPENDIX 129 viii LIST OF FIGURES Figure 1.1 Chemical structures of 1.1-1.5 2 Figure 1.2 Chemical structures of 1.6-1.8 2 Figure 1.3 All new chemical entities, 01/1981-06/2006, by source (N ) 1184 3 Figure 1.4 Chemical structures of 1.9-1.12 4 Figure 1.5 Chemical structures of 1.13-1.15 5 Figure 1.6 Chemical structures of 1.16-1.18 6 Figure 1.7 Chemical structures of 1.19 and 1.20 6 Figure 1.8 Chemical structures of 1.21 and 1.22 7 Figure 1.9 Chemical structures of 1.23 and 1.24 8 Figure 1.10 Chemical structures of 1.25 and 1.26 8 Figure 1.11 Chemical structures of 1.27 and 1.28 9 Figure 1.12 Chemical structures of 1.29-1.31 10 Figure 2.1 Compounds isolated from Symphonia globulifera 17 Figure 2.2 Chemical structure of compound 2.1 20 Figure 2.3 NMR correlations of compound 2.1 21 Figure 2.4 Chemical structures of compound 2.2 and2.3 22 Figure 2.5 Chemical structures of compounds 2.4-2.6 22 Figure 3.1 Compounds isolated from Bussea sp. 34 Figure 3.2 Chemical structures of bussealin A-D (3.1-3.4) 36 Figure 3.3 Chemical structures of bussealin E (3.5) and 3.6 40 Figure 3.4 COSY, HMBC and NOESY correlations of 3.5 40 ix Figure 4.1 Compounds from the genus Leptadenia 53 Figure 4.2 Chemical structures of madagascarensilides A (4.1) and B (4.2) 55 Figure 4.3 a) Key COSY (bold) and HMBC (arrows) correlations for 4.1 b) Key ROESY correlations for 4.1 57 Figure 4.4 Chemical structures of madagascarensilides C (4.3) and D (4.4) 63 Figure 4.5 a) Key COSY (bold) and HMBC (arrows) correlations for 4.3 b) Key ROESY correlations for 4.3 64 Figure 5.1.